Vol. 74, No. 14 (2025)
2025-07-20
REVIEW
2025, 74 (14): 148803.
doi: 10.7498/aps.74.20250591
Abstract +
As the core power unit of new energy vehicles, the accurate modeling of power batteries is of great significance for evaluating their operating status, diagnosing faults throughout their lifecycle, and ensuring safety control under multiple operating conditions. The electrochemical model represented by the P2D model serves as a mechanistic model that can characterize the internal electrochemical reaction process of batteries on a microscale. Its accurate description of the aging and heating behavior of power batteries is an important basis for evaluating the capacity degradation, increase in internal resistance, uneven heating, and inconsistent performance of battery modules. The paper summarizes the latest advances in electrochemical modeling of lithium-ion power batteries, analyzes the coupling methods and application status of electrochemical models with equivalent circuit models, aging models, and thermal models, and focuses on the problem of numerous parameters and difficult identification of electrochemical models. In this paper, the advantages and disadvantages of the single particle model, single particle model with electrolyte, electrochemical mean model, solid-liquid phase reconstruction model, one-dimensional electrochemical model and other methods are compared with each other and analyzed for reducing the order of power battery electrochemical models, the key difficulties in characterizing electrochemical model order reduction are pointed out, and the research trends of electrochemical model reduction order reconstruction methods are prospected, in order to provide direction for the research on electrochemical model reduction order reconstruction of power batteries.
INSTRUMENTATION AND MEARMENT
2025, 74 (14): 148703.
doi: 10.7498/aps.74.20250211
Abstract +
Terahertz (THz) time-domain spectroscopy and imaging techniques on a nanoscale are crucial for material research, device detection, and others. However, traditional far-field THz time-domain spectroscopy faces inherent diffraction limitations, which limits the applications of carrier dynamics analysis that require femtosecond time resolution and nanoscale spatial precision. We present a scattering-type scanning near-field optical microscopy that overcomes these limitations by combining ultrafast THz time-domain spectroscopy with atomic force microscopy (AFM). The utilization of the near-field interaction between the needle tip and the sample surface is demonstrated to facilitate the study of semiconductor materials and devices by using static THz spectroscopy with a lateral spatial resolution of ~60 nm. This, in turn, enables the acquisition of static THz conductivity distributions of the semiconductor materials. Additionally, it facilitates the acquisition of transient conductivity distributions of semiconductor materials and laser THz emission ultrafast via photoexcited transient carrier kinetic processes, which provides substantial support for studying the performances of materials and devices in nanometer spatial resolution, ultrafast time resolution, and THz spectroscopic imaging. The experimental results show that the system has a signal-to-noise ratio as high as 56.34 dB in the static THz time-domain spectral mode, and can effectively extract the fifth-order harmonic signals covering the 0.2–2.2 THz frequency band with a spatial resolution of up to ~60 nm. Carrier excitation and complexation processes in topological insulators are successfully observed by optical pump-THz probe with a time resolution better than 100 fs. Imaging of SRAM samples by the system reveals differences in THz scattering intensity due to non-uniformity in doping concentration, thereby validating its potential application in nanoscale defect detection. This study not only provides an innovative means for studying the nanoscale electrical characterization of semiconductor materials and devices, but also opens a new way for applying the THz technology to interdisciplinary subjects such as nanophotonics and spintronics. In the future, by integrating the superlens technology, optimizing the probe design, and introducing deep learning algorithms, it is expected to further improve the temporal- and spatial-resolution and detection efficiency of the system.
GENERAL
2025, 74 (14): 140201.
doi: 10.7498/aps.74.20250071
Abstract +
This paper adopts the phase-field based lattice Boltzmann (LB) method to study the dynamic behaviors of soluble surfactant-laden droplets in a uniform electric field. First, two benchmark problems including the surfactant concentration distribution on a static droplet and the deformation of a leaky dielectric droplet in an electric field, are used to validate the reliability of the LB method. Then, we investigate the deformation, breakup, and coalescence behaviors of surfactant-laden droplets in an electric field. The obtained results are shown below. 1) Regarding deformation, the single droplet exhibits two distinct deformation modes: Prolate and oblate shapes. A higher electric capillary number and a higher concentration of bulk surfactants both promote greater droplet deformation. 2) Regarding breakup, a single droplet exhibits two distinct breakup modes: filamentous breakup and conical jetting breakup. Droplets containing surfactants are more like to break up. Specifically, surfactants reduce the retraction degree of the main droplet after filamentous breakup, while increasing the number of satellite droplets formed at the ends of the main droplet after jetting breakup. 3) Regarding coalescence, the double droplets exhibit two distinct processes: deformation coalescence and attractive coalescence. A higher electric capillary number facilitates droplet coalescence. Surfactants promote the deformation coalescence while retarding attractive coalescence, but the promotional effect dominates. Consequently, a higher concentration of bulk surfactants will enhance the tendency of droplet coalescence.
2025, 74 (14): 140202.
doi: 10.7498/aps.74.20250409
Abstract +
2025, 74 (14): 140301.
doi: 10.7498/aps.74.20250302
Abstract +
With the discovery of two-dimensional materials like graphene, the relativistic two-dimensional Dirac equation has received increasing attention from researchers. Accurately solving the Dirac equation in electromagnetic fields is the foundation for studying and manipulating quantum states of Dirac electrons. Sectioned series expansion method is successful and accurate in solving Schrödinger equation under complex electromagnetic fields. Dirac equation is a system of coupled first-order differential equations with undermined eigenvalues, and it is more difficult to solve. By applying the sectioned series expansion principle to Dirac equation and conducting series expansions in regular, Taylor and irregular regions, we obtain an accurate method with wide applicability. With the method, a universal criterion for bound states of Dirac electrons in electromagnetic fields is derived and the energy levels and wave functions of bound states can be accurately calculated. The criterion given in the main text body shows that the magnetic field and mass field help to confine Dirac electrons while the electric field tends to deconfine them due to Klein tunneling. When the highest power of the electric potential is equal to that of the magnetic vector potential or the mass field, confined-deconfiend states depend on the comparison of their coefficients. We apply the method to two cases: one is massive Dirac electron in Coulomb electric potential (relativistic two-dimensional hydrogen-like atom) and the other is Dirac electron in uniform mangetic field (mangetic vector potenial is A = 1/2Br) and linear electric potential V = Fr. The energy levels of the hydrogen-like atom are calculated and compared with analytical solutions, demonstrating the exceptional accuracy of the method. By solving Dirac equation under uniform magnetic field and linear electric potential, the method proves to be broadly applicable to the solutions of Dirac equation under complex electromagnetic fields. Under uniform magnetic field B and V = Fr, as the F increases, level orders of negative energy states change and at the critical point F = 0.5B, the bound states of positive ones still exist while only certain negative ones can exist on condition that their energies exceed zero. The sectioned series expansion method provides an effective computational framework for Dirac equation and it deepens our understanding of relativistic quantum mechanics.
2025, 74 (14): 140302.
doi: 10.7498/aps.74.20250268
Abstract +
Based on the basic principles of quantum mechanics, quantum key distribution (QKD) provides unconditional security for long-distance communication. However, existing QKD with relevant source protocols have limited tolerance for source correlation, which greatly reduces the key generation rate and limits the secure transmission distance, thereby limiting their practical deployment. In this work, we propose an improved QKD with correlated source protocol to overcome these limitations by discarding the traditional loss-tolerant security frameworks. Our approach adopts the standard BB84 protocol for the security analysis, under the assumption that the source correlation has a bounded range and characterized inner product of the states. We theoretically analyze the performance of the improved protocol at different levels of source correlation and channel loss. Numerical simulations show that our protocol achieves a much higher secret key rate and longer transmission distance than traditional schemes. In the case of typical parameters and 0 dB loss, our protocol achieves about 1.5–3 times improvement in secret key rate. Additionally, the maximum tolerable loss is enhanced by about 2–6 dB. This highlights a promising direction for enhancing the robustness and practicality of QKD with correlated sources systems, paving the way for their deployment in real-world quantum communication networks.
2025, 74 (14): 140303.
doi: 10.7498/aps.74.20250458
Abstract +
Hyperentanglement, as a high-dimensional quantum entanglement phenomenon with multiple degrees of freedom, plays a critical role in quantum communication, quantum computing, and high-dimensional quantum state manipulation. Unlike entangled states in a single degree of freedom, hyperentangled states establish entanglement relationships simultaneously in multiple degrees of freedom, such as polarization, path, and orbital angular momentum. Through entanglement-based distribution techniques, high-dimensional quantum information networks can be constructed. On this basis, a fully connected quantum network with hyperentanglement is constructed in this work, and the polarization and time-bin degree-of-freedom hyperentanglement is realized through the process of second-harmonic generation and spontaneous parametric down-conversion in periodically poled lithium niobate (PPLN) waveguide cascades. The hyperentangled state is then multiplexed into a single-mode fiber by using dense wavelength division multiplexing (DWDM) technology for transmission to terminal users. The quality of the entangled states in the two degrees of freedom is characterized using Franson-type interference and photon-pair coincidence measurement techniques. Polarization entangled states are subjected to quantum state tomography, and entanglement distribution technology is employed to achieve long-distance distribution and quantum key transmission within the network. Experimental results show that the two-photon interference visibility of both polarization and time-bin entanglement is greater than 95%, demonstrating the high quality of the hyperentanglement in the network. After 100-km-entanglement distribution, the fidelity of the quantum states in both degrees of freedom remains above 88%, indicating the effectiveness of long-distance entanglement distribution in this network. Additionally, it is verified that this network supports the distribution of quantum keys over a distance of more than 50 km between users. These results confirm the feasibility of a fully connected quantum network with hyperentanglement and demonstrate the potential for constructing large-scale metropolitan networks by using hyperentanglement. As a higher-dimensional entanglement, hyperentangled states can significantly enhance the capacity and efficiency of quantum information processing. Although the quantum communication is still in its early stages of development, achieving stable storage and transmission of entangled states in large-scale metropolitan networks remains a great challenge. By utilizing the frequency conversion properties and high integration characteristics of the periodically poled lithium niobate waveguides, the three-user hyperentangled quantum network constructed in this work provides a new solution for developing the large-scale metropolitan networks with high-dimensional quantum information networks. It is expected to provide a new platform for quantum tasks such as superdense coding and quantum teleportation.
2025, 74 (14): 140701.
doi: 10.7498/aps.74.20250212
Abstract +
Femtosecond laser excited terahertz waves have been widely used in various fields. Herein, we demonstrate a novel method to generate terahertz radiation from a terahertz electro-optic crystal excited by infrared supercontinuum radiation (wavelengths > 1 μm), which is produced via the interaction between a femtosecond laser and a transparent solid medium. This approach yields single-cycle, low-frequency, broadband terahertz radiation. In the femtosecond laser-induced ionization process in a medium, both infrared supercontinuum radiation and terahertz radiation are simultaneously generated. When the resulting infrared supercontinuum radiation and terahertz radiation concurrently enter into an electro-optic crystal, the presence of the infrared supercontinuum radiation may interfere with the detection of the intrinsic terahertz radiation. By filtering the infrared supercontinuum radiation with narrowband filters, a new strategy is proposed for investigating the response of the electro-optic crystal in infrared spectral region.
2025, 74 (14): 140702.
doi: 10.7498/aps.74.20250369
Abstract +
In high-energy density physics (HEDP) experiments, accurate diagnostics of physical parameters such as electron temperature, plasma density, and ionization state are essential for understanding matter behavior under extreme conditions. In these cases, X-ray spectroscopic technique, especially those using crystal spectrometers, is widely used to achieve high spectral resolution. However, a common challenge in such experiments lies in the inherent low brightness and poor spatial coherence of laboratory-based X-ray sources, which limit photon throughput, thus the diagnostic accuracy. Therefore, improving the X-ray optical transmission efficiency between the source and the detector is a key step to improve the performance of the whole system. Capillary X-ray optics, which function based on the principle of total internal reflection within hollow glass structures, provides a promising avenue for beam shaping, collimation, and focusing in the soft-to-hard X-ray range. These optical devices are usually divided into polycapillary type and monocapillary type. While polycapillary optics are composed of numerous micro-channels and used primarily for collimating or focusing divergent X-rays, monocapillary lenses—consisting of single curved channels—provide more precise beam control and are particularly suitable for customized X-ray pathways. Depending on the curvature of the inner reflective surface, monocapillaries are classified into conical, parabolic, and ellipsoidal geometries. In this study, we propose and analyze a novel design of a large-caliber conical glass tube, specifically tailored to address the issue of low light utilization in multi-channel focusing spectrographs with spatial resolution (FSSR). The proposed conical glass tube is made of a single large-diameter capillary structure, simplifying alignment requirements and reducing the surface manufacturing precision typically required by complex aspheric lenses. Its geometric configuration enables X-rays from extended or weak sources to be redirected and controlled to convergef, thereby improving photon collection without significantly altering beam divergence. To quantify the performance of this optical system, we develop a detailed mathematical ray-tracing model and implement it in MATLAB. The model combines physical parameters such as capillary inner diameter, taper angle, reflection loss, and source-detector geometry. Numerical simulations show that compared with traditional flat or slit based systems, the new conical design improves source utilization efficiency by 3.1 times. Furthermore, the lens exhibits a ring-shaped enhancement region in the output intensity profile, which can be regulated by adjusting the capillary geometry and source positioning. This feature enables the spatial customization of the beam profile, thereby facilitating optimized coupling with downstream spectroscopic components or imaging systems. In conclusion, the proposed large-aperture conical monocapillary X-ray lens provides a practical and efficient solution for enhancing X-ray optical transport in low-brightness source environments. Its simple construction, tunable focusing characteristics, and compatibility with diverse X-ray source types make it a compelling candidate for integration into a high-resolution X-ray diagnostic system, particularly in HEDP and laboratory-scale X-ray spectroscopy. This work not only introduces a novel optical approach but also provides a robust theoretical and simulation framework for guiding future experimental design and application of capillary-based X-ray optics.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
2025, 74 (14): 141201.
doi: 10.7498/aps.74.20250448
Abstract +
The channel plasma characteristics of an artificially triggered lightning in Guangdong, China, are analyzed using slit-free spectroscopy technology. Based on spectral diagnostic methods, the maximum and minimum values of the triggered lightning channel current are determined to be about 30.9 kA and 25.6 kA (minimum), respectively, and the current is simulated using a modified transmission line model with linear current decay (MTLL). To investigate the electric field distribution, the finite-difference time-domain (FDTD) method and transmission line (TL) model are employed. At a distance of 58 m, assuming a return stroke velocity of 1.3 × 108 m/s, the TL-predicted radiation electric field deviates from experimental electric field, but is very close to the FDTD-simulation of the vertical electric field. Moreover, the analyses of magnetic fields at 58 m, 90 m, and 1.6 km are compared using FDTD simulations, dipole approximation, and charge magnetic field limit (CMFL) estimation. The discrepancies between calculated value and experimental values appear at 58 m and 90 m, which may be due to the near-field interference and measurement limitation. However, they become small at 1.6 km. This work is helpful for the study of lightning electromagnetic field properties and spectral diagnosis.
NUCLEAR PHYSICS
2025, 74 (14): 142101.
doi: 10.7498/aps.74.20250451
Abstract +
The properties of the color-flavor-locked (CFL) quark matter under strong magnetic fields at finite temperatures within a quasiparticle model are investigated in this work. Our results indicate that CFL quark matter pressure becomes anisotropic under strong magnetic fields, while its equation of state (EOS) and equivalent quark mass are both strongly affected by temperature, energy gap constant Δ, and strong magnetic field inside the CFL quark matter. The equivalent quark mass of CFL quark matter decreases with temperature and magnetic field strength increasing, which implies an inverse magnetic catalysis phenomenon. The results also indicate that the entropy per baryon of the CFL quark matter increases with temperature rising and decreases with Δ increasing. Furthermore, the properties of CFL magnetars in different isentropic stages are studied. The star mass and radius depend primarily on the strength and orientation of magnetic fieldinside the CFL magnestars. The maximum star mass increases with entropy per baryon increasing, while the star matter temperature rises at high isentropic stage. Moreover, the polytropic index of the CFL quark matter decreases with star mass increasing.
ATOMIC AND MOLECULAR PHYSICS
2025, 74 (14): 143101.
doi: 10.7498/aps.74.20250324
Abstract +
Steam condensation is a common physical phenomenon in nature and plays an important role in various industrial processes. Therefore, the regulation mechanism of steam condensation process has been widely concerned by scholars in recent years. In this paper, the molecular dynamics simulation method is used to study the vapor condensation behavior of copper surface by establishing a secondary microstructure model. The influences of different geometrical characteristics on the condensation process are discussed by analyzing the nucleation and merging time of droplets, the vapor condensation snapshot, the total number of condensed water molecules, and the total number of water molecules in the maximum condensed drop. With the increase of column width or column height ratio, the molecular weight of the total condensed water first increases and then decreases.
ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2025, 74 (14): 144101.
doi: 10.7498/aps.74.20250130
Abstract +
Dielectric laser accelerators (DLAs), as compact particle accelerators, rely critically on their structural design to determine both the energy gain and beam quality of accelerated bunches. Although most existing DLAs are driven by near-infrared lasers with a wavelength of approximately 1 μm, the use of long-wave infrared (LWIR) lasers at a wavelength ten times that of this wavelength indicates that it is possible to achieve excellent beam quality without sacrificing acceleration gradient. To address the lack of optimized structural designs in the LWIR band where long-distance acceleration poses unique challenges—we introduce a deep learning–based design method for LWIR dielectric grating accelerator structures. Our approach integrates geometric parameters, material properties, and optical-field energy metrics into a unified evaluation framework and uses a surrogate model to predict particle energy gain with high precision. Optimal structural parameters are then extracted to realize the final design. The simulation results show that the energy gain is 99.5 keV (a year-over-year increase of 19.9% ), the transmission efficiency is 100%, the beam spot radius of 14.5 μm, and the average beam current is 20.4 fA, which is 6.9 times higher than similar near-infrared gratings, while maintaining equivalent beam brightness. This work provides a feasible technical route for designing high-netgain LWIR dielectric grating accelerators and a novel framework for optimizing the structure of complex optoelectronic devices.
2025, 74 (14): 144201.
doi: 10.7498/aps.74.20250485
Abstract +
Topological pumping based on Thouless pumping can be effectively applied to optical waveguide array systems to achieve robust light manipulation with strong disturbance resistance. One of its typical models, the Rice-Mele (R-M) model, enables directional light field to transmit from the leftmost (rightmost) waveguide to the rightmost (leftmost) waveguide, which can be utilized to realize fabrication-tolerant optical couplers. Adiabatic evolution is a critical factor influencing the transport of topological eigenstates. However, it requires the system’s parameter variation to be sufficiently slow, which leads to excessively long waveguide lengths, limiting device compactness. To reduce the size, non-adiabatic evolution offers a feasible alternative. Meanwhile, the adiabatic properties of topological pumping models introduce new degrees of freedom, expanding possibilities for light manipulation. Based on the R-M model, this work analyzes the relationship between adiabatic property and structure length L, investigates light field evolution behavior when adiabatic condition is violated, and explores the transition from adiabatic to non-adiabatic regimes. When adiabatic condition is satisfied (L1 = 1000 μm), the light field evolution aligns with the eigen edge state. The output mode is manifested as an edge state and localized at the edge waveguide. As length shortens (L2 = 250 μm and L4 = 30 μm), the deviation between light field and eigen edge state arises, and the eigen bulk states get involved in the light field. The output modes are manifested as the superposition of edge state and bulk state, with energy spreading to other waveguides. At a specific length (L3 = 110 μm), the light-field undergoes non-adiabatic evolution: initially deviating from the edge state and later returning to the edge state. This phenomenon is termed adiabatic equivalent evolution. The output mode is localized at the edge waveguide, which is the same as the adiabatic evolution. By analyzing the fidelity between output mode and eigen edge state, we demonstrate that the adiabaticity can effectively regulate fidelity, achieving signal on/off at the edge waveguide. As structural length decreases, fidelity gradually declines and exhibits an oscillating behavior. When fidelity approaches to 1, the adiabatic equivalent evolution emerges. The first-order perturbation approximation reveals that these oscillations stem from destructive interference between edge and bulk states, thereby confirming their intrinsic origin in band interference. This mechanism enables eigen edge state output at shorter lengths than adiabatic requirements, providing a reliable approach for miniaturizing devices. Furthermore, the fabrication tolerance is analyzed. Within the whole waveguides width deviation range of –35–+30 nm (relative deviation range of –7%–+6%), the transmission of edge waveguide through the adiabatic equivalent evolution is larger than 0.9. This work analyses light-field evolution process and underlying physics for topological pumping in non-adiabatic regimes, supplements theoretical methods for analyzing non-adiabatic evolution, and provides strategies for achieving eigen edge state output at reduced lengths. This work provides some feasible principles for designing topological optical waveguide arrays, guiding the development of compact and robust on-chip photonic devices such as optical couplers and splitters, which have broad application prospects in integrated photonics.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2025, 74 (14): 148702.
doi: 10.7498/aps.74.20250433
Abstract +
The rapid monitoring devices, but there are still challenges in achieving medical-grade accuracy in quantitative pulmonary function assessment. This study integrates water molecule-responsive flexible sensing technology, wearable devices, and cloud-based intelligent analysis platform to develop the first medical-grade flexible respiratory sensing system (SFMS). By utilizing the synergistic effect of bionic microcavity differential pressure sensing and humidity-sensitive interfaces, combined with a pressure difference-flux dynamic model, the system can simultaneously resolve peak expiratory flow (PEF) and forced vital capacity (FVC), accurately obtaining core pulmonary function indicators such as FEV1/FVC. Clinical validation of 454 cases demonstrates high consistency with gold-standard spirometry (intraclass correlation coefficient [ICC] = 0.93–0.97), with a sensitivity of 89.7% and specificity of 92.3% in differentiating chronic obstructive pulmonary disease (COPD) from asthma. Technologically, this work pioneers a medical-grade flexible sensor for quantitative pulmonary testing, and eliminates dependence on specialized operators through an embedded edge computing architecture that supports real-time cloud data interaction. The system establishes disease-specific profiles through multi-parametric physiological correlation analysis. Practically, its low cost, portability, and user-friendly operation facilitate seamless integration into primary healthcare and home health management, providing technical tools for hierarchical diagnosis and treatment of chronic respiratory diseases. Aligned with WHO's Respiratory Health Action Plan, this innovation enables universal monitoring to advance early screening and long-term disease management. As this innovation possesses significant clinical translation potential, it provides a groundbreaking solution for building a comprehensive prevention and control framework for respiratory diseases.
